This application claims the priority of German Patent Application No. 199 56 893.6, filed in Germany, Nov. 26, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a cooling circuit for an internal combustion engine, with a main heat exchanger for cooling the cooling medium circulating in the cooling circuit, with a secondary heat exchanger for the heating of heating air to be supplied to a vehicle interior and with a thermostatic valve.
German Patent Document DE 195 39 605 A1 discloses a heating heat exchanger system which is connected to the cooling system of an internal combustion engine and serves for vehicle heating. Hot cooling medium coming from an internal combustion engine is supplied via a supply line to a thermostatic valve which returns this cooling medium to the engine either indirectly via a vehicle radiator during normal operation or directly via a short-circuit line in a warm-up phase of the engine. Arranged in the supply line to the thermostatic valve is a heat exchanger serving for heating a closed heating circuit in which a vehicle interior heating system is arranged. In this heating circuit, a separate pump is arranged, which drives a heat transfer medium in the heating circuit as a function of the heating capacity required.
German Patent Document DE 195 06 935 C1 discloses a cooling circuit for an internal combustion engine of a motor vehicle, said cooling circuit having an open heating circuit for heating a heating body for heating the interior of a vehicle. In this case, some of the heated cooling fluid is extracted directly at the internal combustion engine for the heating circuit and returned to the cooling circuit again.
Cooling circuits of this type with an open or a closed heating circuit have a complicated design which, particularly because of the pump additionally required, is relatively costly.
European Patent Document EP 0 174 800 A1 discloses a cooling circuit which manages without a second pump. A thermostatic valve is shown there, which has a first and a second inlet and a first and a second outlet. The first inlet and the second outlet are tied into a cooling circuit of an internal combustion engine, whilst the second inlet and the first outlet are connected to an inlet and an outlet of a heat exchanger which serves for the heating of air to be supplied to a vehicle interior. The thermostatic valve connects the first inlet to the first outlet and the second inlet to the second outlet, so that the cooling medium is extracted from the cooling circuit and is returned to the cooling circuit again via the heat exchanger. As a function of the pressure gradient prevailing in the cooling circuit between the first inlet and second outlet, the actuator in the thermostatic valve opens to a greater or lesser extent a bypass which allows a direct throughflow from the first inlet to the second outlet, the heat exchanger being bypassed.
In an arrangement of this type, however, the volumetric flow of the cooling medium flowing through the internal combustion engine depends on the switching position of the thermostatic valve. However, changes in throughflow quantities, which may occur simultaneously with a change in temperature of the cooling medium flowing through the engine, are undesirable, since this may lead to high thermal expansion loads on the internal combustion engine and entail the risk of cracking.
Furthermore, the pressure gradient between the first inlet and the second outlet depends, in this case, on the pumping capacity of a pump driving the cooling medium and therefore normally on the rotational speed of the internal combustion engine correlated to this pumping capacity, so that, with an increase in rotational speed, the bypass is opened more and more and the flow through the heat exchanger is blocked more and more. Beyond a specific engine rotational speed, the flow through the heat exchanger is then blocked completely, so that, beyond this rotational speed, the heating of the vehicle interior no longer functions.
The present invention is concerned with the problem of producing a cooling circuit of the type mentioned in the introduction, in such a way as to provide a relatively cost-effective design which ensures heating via the secondary heat exchanger in all the operating states of the internal combustion engine.
This problem is solved, according to the invention, by means of a cooling circuit for an internal combustion engine, comprising:
a main heat exchanger for cooling the cooling medium circulating in the cooling circuit,
a secondary heat exchanger for the heating of heating air to be supplied to a vehicle interior, and
a thermostatic valve,
an inlet of the thermostatic valve being connected to an outlet of the internal combustion engine,
a first outlet of the thermostatic valve being connected to an inlet of the main heat exchanger,
an outlet of the main heat exchanger being connected to an inlet of the internal combustion engine,
a second outlet of the thermostatic valve being connected to the inlet of the internal combustion engine via a short-circuit line,
an inlet of the secondary heat exchanger being connected to the second outlet of the thermostatic valve, and
an outlet of the secondary heat exchanger being connected to the inlet of the internal combustion engine,
wherein the thermostatic valve is configured in such a way that the thermostatic valve:
fully opens the first outlet and throttles the second outlet in a first end position corresponding to an engine cooling mode,
opens the first outlet and the second outlet to a greater or lesser extent in intermediate positions corresponding to a mixed mode, and
blocks the first outlet and fully opens the second outlet in a second end position corresponding to a warm-up mode.
The invention is based on the general notion of using a throttled bypass to avoid complete blocking of a valve outlet assigned to the inlet of the secondary heat exchanger. In this way, in any operating phase of the engine, cooling medium can be conducted through the secondary heat exchanger, in order to make heating possible. The thermostatic valve outlet throttled for this purpose thus allows a minimum flow of cooling medium to pass through in order to operate the heating system.
According to an advantageous feature of preferred embodiments, the secondary heat exchanger may be arranged in a short-circuit line which, for a warm-up phase, supplies the cooling medium flowing off from the internal combustion engine directly to the internal combustion engine again, the main heat exchanger being bypassed. The thermostatic valve outlet assigned to the short-circuit line is thereby connected to the inlet of the internal combustion engine via the secondary heat exchanger. Such a form of construction is particularly cost-effective, since there is no need for additional lines.
According to a further advantageous feature of preferred embodiments, the individual components of the cooling circuit may be dimensioned and coordinated with one another in such a way that a throughflow resistance between a second outlet of the thermostatic valve and the inlet of the internal combustion engine is approximately equal to a throughflow resistance between a first outlet of the thermostatic valve and the inlet of the internal combustion engine. The volumetric flow flowing through the internal combustion engine is thus independent of the position of the thermostatic valve. The risk of damage to the internal combustion engine by a simultaneous jump in the volumetric flow and in the temperature of the cooling medium can be reduced as a result.
Further important features and advantages of the invention may be gathered from the claims, the drawings and the accompanying FIG. descriptions with reference to the drawings.
It goes without saying that the features mentioned above and those still to be explained below can be used not only in the combination specified in each case, but also in other combinations or alone, without departing from the scope of the present invention.
Preferred exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.